1. Field of the Invention
The present invention relates to inspection equipment for a screw part of a bottle-can.
Priority is claimed on Japanese Patent Application No. 2011-126218, filed Jun. 6, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
A can having a bottle-shape of aluminum alloy in which a cap is screwed on a mouth section having a screw is known as a container filled with contents such as drinks. The bottle-can is manufactured by forming an aluminum alloy sheet into a closed-end cylindrical body which has a bottom plate and a cylindrical side surface in one piece by performing drawing processing and ironing processing (i.e., DI forming); coating an inner surface and an outer surface of the close-ended cylindrical body; forming a shoulder and the mouth section by performing so-called neck-in processing on an opening portion; and performing screw-forming processing, curl-forming processing and the like on the mouth section.
A cap which is attached on the bottle-can is formed to have a peripheral wall with a straight cylindrical shape in a prior state to an attachment on the bottle-can. After placing the cap on a mouth section of the bottle-can, by deforming the cap so as to follow a screw part formed on the mouth section, a screw part is formed on the cap and the bottle-can is sealed with the cap. Accordingly, the shape of the screw part of the bottle-can decides the screw part of the cap which is attached subsequently.
Therefore, for a steady cap-openability, it is important for the screw part of the bottle-can that, for example: a position of a thread-starting part and a position of a thread-ending part are precise, a lead angle of the screw part is constant, and there is no deformation such as a bend or the like and linearity is excellent. Furthermore, it is required that the bottle-cans having a defect on the above properties are reliably eliminated as defective products by detecting in an inspection process.
As an inspection method for the screw part of the bottle-can, for example, Patent Document 1 discloses a method by: catching an outline of the bottle-can from an image of the bottle-can by illuminating from a rear, setting a top surface of an aperture section as a standard measuring-line based on the outline, and measuring dimensions of parts of a bottle-can based on the standard measuring-line.
Patent Document 2 discloses that: a thread-starting part of a bottle-can is colored beforehand so that a circumferential position of the bottle-can is specified by detecting the thread-starting part, and then parts of the bottle-can are measured from an outline image by measuring equipment disclosed in Patent Document 1.
Patent Document 3 discloses that: imaging an outline image of a bottle-can while rotating the bottle-can, tracking a measuring area with respect to a movement of a point of a thread ridge which moves along with the rotation, and obtaining position coordinates of the point of the thread ridge in the measuring area each at the rotation.